In conventional vehicle automatic transmissions of the torque converter type, a drive shaft extends from the torque converter into the transmission housing to a unit having one or more clutch drums around which are arranged either single-wrap or double-wrap brake bands. It is the function of the brake band, through the function of suitable hydraulic controls to effect gear changes and also control the direction of rotation of the output shaft from the transmission to the differential for the driving wheels of the vehicle.
The present invention is an improvement in the anchor or reaction bracket of a transmission brake band and will be described in an embodiment intended to be illustrative and is not intended to be limiting upon the use of this invention with transmission brake bands of all designs and styles.
Single-wrap brake bands are currently available in two distinct styles. The most commonly known single-wrap brake band is usually formed from a strip of sheet steel or similar material, having at its ends brackets formed from separate forgings, castings or stampings. The brackets are suitably secured to the strap of material by spot welding or similar methods as shown in U.S. Pat. No. 3,732,954. More recently, a unitary single-wrap brake band has been designed which utilizes a single piece of material wherein the brackets are extruded or formed from double thicknesses of the base metal at the ends of the strap member. An example of a brake band of this type of structure is disclosed in U.S. Pat. No. 5,078,237 issued from the grandparent '161 application of this application.
Regardless of how the brake band and bracket members are formed, it is a requisite that each brake band have an actuation or apply end for receiving an apply piston and a reaction or anchor end which is operatively connected to a reaction member located in the transmission. Various types of automatic transmissions utilize different types of reaction members. Some reaction members may be of the tangential type which comprise a stationary plunger or stop member acting against the anchor end of the brake band, while other reaction members may be the reaction pin type where the pin extends perpendicular to the clutch drum and strap member and extends into a reaction opening located in the anchor bracket of the brake band.
Where a reaction pin is used as the reaction member in the transmission band, a "volcano" type reaction bracket is commonly provided to engage the reaction pin. A typical volcano bracket consists of an extruded opening extending radially outwardly from the reaction bracket of the band. Alternatively, a bushing secured to the bracket may have a reaction opening formed therein to receive the free end of the reaction pin, thus providing the anchored end of the brake band during use of the band in the automatic transmission. The opposite or apply end of the band is provided with an apply bracket for engaging the end of the apply plunger in the transmission that is hydraulically controlled to urge the band ends together and tighten the brake band around the clutch drum, thus stopping the rotation of the drum or otherwise altering the rotation of the drum or other member to change the gear ratio or alter the direction of rotation of the output shaft. Due to the close tolerances required for proper function between the free end of the reaction pin and the opening of the volcano, many problems have been encountered in which the volcano opening fails prematurely during testing or operation of transmission. For instance, if the reaction pin is not fully engaged with the volcano opening the open edges of the volcano may chip, splinter, and crack.
The '237 patent approaches the stress failure problems of such volcano brackets by providing a single piece brake band with an anchor embossment extruded from a double thickness of the strap material to produce a volcano type reaction bracket at one end of the brake band. The strap material is folded upon itself to form the double-layer and the volcano opening is formed by piercing the double layer of material to extrude the layers and form a tapered opening. The two layers of strap material are then secured together by clinch fastening, spot welding or other adequate means.
While the extruded volcano opening has provided for enhanced strength characteristics and has significantly reduced the number of stress failures in such volcano anchor brackets, it remains desirable to further reduce the risk of failure of volcano-type reaction openings. Problems with stress fractures and failures are still encountered, especially in situations where the reaction pin is not fully inserted through the opening and forces are exerted at the upraised edges of the opening.
Therefore, it is an object of this invention to provide a reaction bracket having enhanced strength characteristics to overcome the possibility of premature failures of the brake band. The present invention achieves this goal by increasing the strength of the bracket and reinforcing the volcano so that premature failure of the bracket is quantitatively lessened.